Mississippi Valley-type Deposits Research Articles

Industrial rocks and minerals of Jordan: a review

Mineral resources of Jordan were utilized by different civilizations since prehistoric time. The following review highlights important and strategic commodities that are found in a small country with a potential promising future. Jordan is rich in its diverse industrial rocks and mineral resources that are part of the whole stratigraphic sequence from the Precambrian basement complex to the Recent sediments. Such diversity of resources enables Jordan to be not only a host of some unlimited resources but also a natural geology museum. The known commodities include, among others, phosphates, bituminous marl (oil shale), tar sand, varicolored marbles, travertine, radioactive minerals, building and construction materials, clays and clay minerals, diatomaceous earth, porcelanite, Dead Sea brines, rock salt, chalk, limestone, gypsum, glass sand, basalt, pyroclastics, zeolites, granite, copper, manganese, gold, etc. Some of these commodities are unique and unusual in its mineralogy, chemistry, and origin. A novel geopolymerization process was developed in Jordan to produce green building materials (geopolymers) by using Jordanian kaolinite. Volkonskoites (Cr-rich smectite) of Jordan act as a sink for hazardous elements. Varicolored marbles of Jordan are considered a natural cement factory and are analogs of cementitious repositories with the highest alkaline circulating waters in the World. New minerals were reported for the first time, some of which are only known in meteorites. The unusual enrichment of the reduced sensitive elements (RSE) in the oil shale (similar to the source of Mississippi Valley-type deposits) makes it unique as a potential source of these strategic elements.

Rb-Sr isotopic age, S-Pb-Sr isotopic compositions and genesis of the ca. 200 Ma Yunluheba Pb-Zn deposit in NW Guizhou Province, SW China

Over 400 carbonate-hosted Pb-Zn deposits in the western Yangtze block constitute the giant Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province. The majority of Pb-Zn deposits hosted in Devonian carbonates are characterized by low δ34S values, causing debates on their ore genesis. To address this issue, the Yunluheba Pb-Zn deposit is chosen as a case study. Ore bodies of this deposit are hosted in middle Devonian carbonates. Ore minerals are sphalerite, galena and pyrite. Sphalerite Rb-Sr dating yields an isochron age of 206.2 ± 4.9 Ma, consistent with ages of most Pb-Zn deposits in the SYG province, arguing for a regional intensive Pb-Zn mineralization event during the late Indosinian orogeny. Sulfides have Pb isotopic compositions that form a linear trend above the average crustal Pb growth curve in the 207Pb/204Pb vs. 206Pb/204Pb plot. Moreover, Pb isotopic ratios are consistent with the Devonian to Permian carbonates’ age-corrected Pb isotopic ratios, suggesting mixed crustal Pb sources with the majority of Pb derived from country rocks. Combined with initial 87Sr/86Sr ratios of sphalerite, approximately equal to 87Sr/86Sr200Ma ratios of the D-P carbonates, ore-forming metals are considered to have been derived mainly from ore-hosting rocks. Sulfides’ δ34SCDT values range mainly from −2.0‰ to 2.9‰, interpreted to be a result of mixing by syn-sedimentary pyrite originated biogenic S and thermochemically reduced S. We conclude that the Yunluheba deposit and other Pb-Zn deposits in the SYG province should belong to Mississippi Valley-type deposits.

Experimental study on fluid migration mechanism related to Pb–Zn super-enrichment: Implications for mineralisation mechanisms of the Pb–Zn deposits in the Sichuan–Yunnan–Guizhou, SW China

This study focuses on the problem of Pb–Zn super-enrichment, and is based on a new conceptualisation of fluid–rock interactions → change in fluid properties → Pb–Zn hydrolysis → complex instability. Non-magmatic, epigenetic, hydrothermal Pb–Zn deposits in carbonates were used to perform Pb–Zn hydrolysis experiments under normal pressure. Lead–zinc fluid and carbonate interaction experiments, as well as Pb–Zn hydrolysis kinetics experiments during fluid–rock interaction, were performed analyse the roles of pH and fluid–rock interactions in Pb–Zn transport and precipitation, and to investigate the main reasons for the grade disparity between Mississippi Valley-type (MVT) deposits and Pb–Zn deposits found in the Sichuan–Yunnan–Guizhou region of China. Our results show that a pH = 4 is the threshold value for the large-scale hydrolysis of Pb and Zn. When reactions between acidic solutions containing Pb and Zn (pH = 1.0–6.0) and carbonate rocks (i.e., the surrounding rock) reach equilibrium, the final pH of the solution stabilises at 5.2–6.2, which is not associated with the lithology of the surrounding carbonate rocks (dolomite or limestone), crystallite size or the initial pH of the solution, and is negatively correlated with rock particle size. Fluid–rock interactions cause pH to increase, Pb and Zn to partially hydrolysis, and minerals to precipitate, with the maximum precipitation rate reaching ~20%. When hydroxide precipitates are mixed with fluids containing reduced S, the precipitates are converted into sulphides. Thus, mineralisation fluid pH, the driving force of fluid migration, Pb–Zn hydrolysis, and fluid–rock interactions combine to restrict the formation of Pb–Zn deposits in carbonates. Among these factors, differences in Pb–Zn hydrolysis are the main causes of disparities among deposit grades. This study not only provides an in-depth consideration of the geochemical behaviour of Pb and Zn in a carbonate-hosted hydrothermal system, but also serves to clarify the mineralisation mechanisms of Pb–Zn deposits in the Sichuan–Yunnan–Guizhou region.

Geochemical investigations of the Woodford–Chattanooga and Fayetteville Shales: Implications for genesis of the Mississippi Valley–type zinc–lead ores in the southern Ozark Region and hydrocarbon exploration

The relationship between base metal deposits, especially Mississippi Valley–type (MVT) Pb–Zn deposits, and hydrocarbons is not well constrained. This is despite the fact that hydrocarbons generally occur in MVT deposits; the ores are emplaced in the same temperature range as hydrocarbon maturation and migration, and the deposits commonly occur in proximity to metal-rich black shales. Better understanding should lead to better exploration models for both hydrocarbons and MVT deposits. This connection is better understood with the help of Pb isotope patterns. Sphalerite Pb isotope compositions from the northern Arkansas and Tri-State mining districts and Woodford–Chattanooga and Fayetteville Shales were determined to assess the potential of shales as source rocks for the ore metals. The ores in both districts have a broad range of Pb isotope ratios and define linear trends, suggesting mixing of Pb from two distinct end members. Current results and previous depositional environment studies indicate the following: (1) shales deposited mainly under nonsulfidic anoxic conditions represent the less radiogenic end member, or (2) shales are the only source of ore metals. Given the array of organic molecules, each with their own thermochemical range, and the ways metals can be associated with them, the release of metals may cover varying ranges. Thus, the compositions of the released fluids would change through time and not have a single static composition, closely approximating the isotopic composition of the released metals at various times. Mineralization derived from a dynamically evolving fluid may show apparent end members, without the need to call on mixing of fluids from separate sources.

Sediment-hosted Pb–Zn deposits in the Tethyan domain from China to Iran: Characteristics, tectonic setting, and ore controls

The Tethyan domain from China to Iran hosts many important sediment-hosted Pb–Zn deposits but most have been poorly documented. This study summarizes the salient features of these deposits and discusses the type of ore, tectonic setting, and important ore controls, on the basis of new geological observations and previous publications. The Tethyan domain is characterized by the young and extensive Himalayan–Tibetan and Zagros orogens that formed through collisions between the India/Arabia and Eurasia continents since the Late Cretaceous or early Cenozoic. Abundant Mississippi Valley-type (MVT) and subordinate clastic-dominated (CD, also known as SEDEX) Pb–Zn deposits occur in this domain, including in central and eastern Himalayan–Tibetan orogen in China, the Indian passive margin in southern Pakistan, and various tectonic units of Iran. Economically important deposits contain 0.1–21 Mt Pb + Zn and have total metal resources of ∼75 Mt with ∼48% being oxidized ores. All major deposits known in this domain are MVTs (i.e., the Jinding, Huoshaoyun, Mehdiabad, and Angouran deposits).Mississippi Valley-type Pb–Zn deposits occur in continental-collision-related fold-and-thrust belts and forelands, where deposits are mostly located on the margin of the Eurasian continent, with some in the Indian and Arabian continental margins. Clastic-dominated Pb–Zn deposits occur in central Iran and southern Pakistan, hosted by deep-water siliciclastic sequences of the early Cambrian rifted continental margin of Gondwana and the Jurassic passive continental margin of India, respectively. The youngest mineralized rocks and ages constrain that some important MVT deposits (e.g., the Jinding, Chaqupacha, and Angouran deposits) were formed after a main phase of regional compression, during a regional, large-scale strike-slip or crustal-extension stage in a continental collision setting. In sense of lithologic structure, important ore controls for MVT deposits include evaporite diapir structure, carbonate/evaporite dissolution–collapse structure, pre-existing barite, and porous dolostone. Much of the primary sulfide ore in this domain has been oxidized by supergene processes. This is particularly pronounced in the newly discovered Huoshaoyun deposit, where almost all sulfides have been oxidized to smithsonite and cerussite. An understanding of tectonic setting, ore controls, and supergene processes is essential in exploring for MVT deposits in this domain.

Petroleum as source and carrier of metals in epigenetic sediment-hosted mineralization

Sediment-hosted ore deposits contribute a significant amount (up to 65%) of the global resources of lead and zinc. Among them, the Mississippi-Valley type deposits and related oil fields often comprise large-scale hydrothermal systems where regional host rocks are stained with disseminated liquid petroleum (crude oil) and other organic compounds. Current models for the formation of those epigenetic Pb-Zn sulphide deposits consider that metals are mostly leached from basement rocks and their detrital erosional products, and transported by oxidized basinal hydrothermal fluids as chloride complexes. Sulphide precipitation mainly occurs when these basinal brines interact with fluids rich in reduced sulphur species produced mostly by thermochemical sulphate reduction (TSR) mediated by hydrocarbons. Here, using organic geochemistry and Pb isotopes, we provide evidence that petroleum and associated water were key for the formation of sulphide mineralization in the world-class sandstone-hosted ore deposit at Laisvall, not only by supplying reduced sulphur but also by contributing metals in significant amounts. The lead originally found in bitumen of the Alum Shale Formation was transported —during an arc-continent collisional event— by liquid petroleum and associated water to the site of sulphide mineralization. The alteration of petroleum by TSR made lead available for precipitation as sulphide. The petroleum-associated lead represents 40 to 60% of the metal budget in the deposit, the remainder being sourced by leaching of basement rocks.

Regional scale prospecting for non-sulphide zinc deposits using ASTER data and different spectral processing methods

ABSTRACT The Ravar-Kuhbanan-Bahabad belt (RKBB) in Central Iran contains several carbonate-hosted non-sulphide Zn (zinc)-Pb (lead) deposits. The Gujer Zn mine area located in the middle of the RKBB was selected as the case study. Due to its large extent, dolomitic envelope in carbonate host rocks can be considered as a more appropriate exploratory target than small Zn-rich gossans or blind karst filling ore. Based on previous studies, the occurrence of red sandstone as a candidate of supplying metal for mineralization and evaporate as sulphate source for mineralized liquids in the vicinity of carbonate rocks can be important exploratory key in the RKBB. Non-sulphide Zn deposits were formed through oxidation of primary Mississippi Valley-type (MVT) deposits in the study area. Remote sensing studies were undertaken using visible to near-infrared (VNIR) and shortwave infrared (SWIR) bands of the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) with the objective of lithological mapping. Five traverse lines containing a total of 81 samples were designed and followed with subsequent chemical analysis, thin section studies, and spectroscopy to verify the results. Two types of carbonates, namely, magnesian dolomite as host rock and surrounding calcitic limestone, were realized through using magnesium oxide (MgO) to calcium oxide (CaO) ratio. Based on spectroscopy studies, calcite and dolomite showed distinct absorption features at 2.35 µm and 2.32 µm, respectively, in ASTER band 8 while a shoulder at 2.25 µm was seen in ASTER band 7 for dolomite. Three image processing methods including spectral angle mapper (SAM), linear spectral unmixing (LSU), and mixture-tuned matched-filtering (MTMF) were applied to separate dolomite and limestone. The accuracy of image classification was numerically estimated using a confusion matrix. Limestone with the accuracy of 95.83% was more precisely enhanced using MTMF method compared to SAM and LSU methods. Highest accuracy of 75% for dolomite was obtained through using LSU method. Red sandstone and evaporate units were classified using MTMF and SAM/LSU methods, respectively. Rock units with the highest accuracy were selected and simply overlain on an image of ASTER in a GIS platform to create the potential map of the study area. Results showed that ASTER data can be successfully used to prepare a potential map for regional scale prospecting for carbonate-hosted non-sulphide Zn-Pb deposits in geological setting and climate condition similar to the RKBB.

Application of mineral norm calculation in the resource evaluation of the sulphide and non-sulphide Zn-Pb mineralisation of the Florida Canyon MVT deposit, Peru

ABSTRACTBoth Zn–Pb hypogene sulphide and Zn supergene non-sulphide mineralisation types occur in the Mississippi Valley-type deposit of Florida Canyon, located in northern Peru. The geometry and spatial relationship between the two ore types are very complex to interpret, when it comes to mineral resource evaluation. An algorithm using the Zn, Pb and S contents is proposed for the calculation of sphalerite, galena and non-sulphide norms in the block model after its conventional ordinary kriging estimation. Model validation was performed by comparing the results of the calculations with available SEM/EDS-MLA data. The results show good correlation between the calculated and the quantitative values, thus accrediting the proposed methodology. The algorithm is simple and fast to use and can be applied to mineral resource evaluation of Zn–Pb MVT deposits associated with non-sulphide mineralisation.

Zinc solubility, speciation and deposition: A role for liquid hydrocarbons as ore fluids for Mississippi Valley Type Zn-Pb deposits

Although the ore fluid for Mississippi Valley Type (MVT) deposits is universally considered to be a basinal brine, the common occurrence of liquid hydrocarbons as inclusions in one of the ore minerals (sphalerite) raises the question of whether liquid hydrocarbons could play a role in metal transport. Here we explore the potential of liquid hydrocarbons to act as an ore fluid by determining the steady-state concentration of zinc in crude oil and evaluating the factors that promote its dissolution. To this end, zinc wires were reacted with a series of oils (labelled oils A, B and C) at 150, 200 and 250 °C, and the steady-state concentration of Zn was determined. Zinc concentrations were observed to increase with temperature and with the Total Acid Number (TAN) of the oils, the latter of which is strongly correlated to the carboxylic acid content of crude oil. Crude oil B, the highest TAN oil, dissolved 1700 ± 0.8 ppm at 250 °C, which is comparable to the highest Zn concentration inferred to have been dissolved in brines interpreted to represent MVT ore fluids. X-ray Photoelectron Spectroscopic (XPS) analyses performed on the residual oil coating the zinc wires after the reaction supported the conclusion that Zn has a strong chemical affinity for carboxylic acids in crude oil. Finally, an experiment designed to precipitate sphalerite crystals from a Zn-rich synthetic oil at room temperature showed that sphalerite precipitation from liquid hydrocarbons proceeds efficiently in a carbonate-buffered, H2S -rich environment.

Major and trace elements and sulfur isotopes in two stages of sphalerite from the world-class Angouran Zn–Pb deposit, Iran: Implications for mineralization conditions and type

The Angouran deposit is the second-largest Zn–Pb deposit in Iran with 4.7 Mt sulfide ore (27.7% Zn, 2.4% Pb, and 110 g/t Ag) and 14.6 Mt nonsulfide ore (28.1% Zn, 4.4% Pb). Various models have been proposed to explain the genesis of sulfide ore in this deposit. Moreover, the mineralization type of its primary sulfide ores remains controversial. The major and trace element concentrations and sulfur isotopic composition of the two stages of sphalerite have been analyzed to constrain mineralization conditions and the genesis. The Angouran deposit, which contains discordant orebodies, is hosted in a Neoproterozoic/Cambrian schist-marble sequence. Two stages of sphalerite have been distinguished: early-stage (S1) red-brown sphalerite and late-stage (S2) honey-yellow sphalerite. Our result shows that, relative to the S2 sphalerite, the S1 sphalerite has higher contents of Fe, Mn, Co, Cu, Ag, Sn, Ga, Sb and In, but lower contents of As and Tl. Time-resolved depth profiles in these sphalerites determined by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses indicate that Fe, Cd, Co, Hg, Mn, Ge, and In are mainly present in solid solution and that Ag, Cu, Pb, As, Ni, Ga, Tl, Sb, and Sn are present in both solid solution and mineral inclusions. Correlation analyses reveal the occurrence of direct substitution mechanisms, such as Zn2+ ↔ (Fe2+, Cd2+) and 2Zn2+ ↔ Ge4++□ (vacancy) as well as coupled substitutions, such as 2Zn2+ ↔ Cu+ + Ga3+, 2Zn2+ ↔ (Cu+, Ag+) + Sb3+, 3Zn2+ ↔ Pb2+ + Tl+ + As3+, 4Zn2+ ↔ Pb2+ + 2As3++□(vacancy) or (Zn2+, Pb2+) ↔ Tl+ + As3+, and 4Zn2+ ↔ Cu+ + (Ga3+, In3+) + Sn4++□(vacancy). Geothermometer studies suggest that sphalerite in the Angouran deposit precipitated from a low-temperature (<200 °C) hydrothermal system. Trace element concentrations also reveal that the estimated average temperature of ore-forming fluid decreases gradually and becomes relatively oxidized from early stage to late stage. The low contents of Mn, and In and Zn/Cd ratios and high contents of Cd and Ge in sphalerite are consistent with those of MVT deposits but are different than that of magmatism-related deposits (e.g., epithermal, skarn, carbonate-replacement, and volcanogenic massive sulfide deposits). Meanwhile, the δ34SV-CDT values of the S1 and S2 sphalerites, which range from 5.1‰ to 10.9‰, are atypical of magma-derived sulfur isotopic compositions. Therefore, the Angouran deposit was formed in a low-temperature (<200 °C) fluid system and can be classified as a Mississippi Valley-type (MVT) deposit.

Fluid inclusions, S isotopes, and Pb isotopes characteristics of the Kuh-e-Surmeh carbonate-hosted Zn–Pb deposit in the Zagros Fold Belt, southwest Iran: Implications for the source of metals and sulfur and MVT genetic model

The Kuh-e-Surmeh Zn–Pb deposit is hosted by Upper Permian carbonate platform in the Zagros Fold Belt of southwestern Iran. The orebody is characterized by massive, vein, and banded textures. It is mostly composed of sphalerite, galena, and pyrite accompanied with minor barite. Homogenization temperatures of fluid inclusions in sphalerite and barite range from 94.7° to 200.0 °C and 93.6° to 198.0 °C, respectively. Fluid salinities of sphalerite- and barite-hosted inclusions vary from 8.1 to 21.3 wt% NaCl equiv. and 10.5 to 22.6 wt% NaCl equiv., respectively. The δ34S values of barite range from 11.2 to 11.9‰, similar to those of gypsum of the Nar Member (+10.9 to +11.7‰) in the Upper Permian sedimentary strata and different from the δ34S values of Jahani Salt Dome gypsum (+29.1 to +30.5‰), indicating that sulfur was derived from the Upper Permian evaporites. The δ34S values of galena and sphalerite range from −1.7 to −15.4‰, compatible with bacterial sulfate reduction (BSR) of the Upper Permian evaporites. The Pb isotopic compositions of galena yield 206Pb/204Pb ratios from 17.942 to 18.340, 207Pb/204Pb ratios from 15.649 to 15.744, and 208Pb/204Pb ratios from 38.186 to 38.458, indicating an upper crustal lead source.Based on ore textures, fluid inclusions, isotope data, and geochemical compositions of sulfide minerals, the Kuh-e-Surmeh sulfide mineralization is believed to have precipitated from low-temperature sedimentary basin brines and should be classified as a Mississippi Valley-type deposit in a salt diapir environment. Mineralization is the result of mixing of hypogene metalliferous fluids with more dilute, H2S-rich fluids during Miocene–Pliocene compression associated with the Zagros Orogeny.

The ore genesis of the Jebel Mecella and Sidi Taya F[sbnd]Ba (Zn[sbnd]Pb) Mississippi Valley-type deposits, Fluorite Zaghouan Province, NE Tunisia, in relation to Alpine orogeny: Constraints from geological, sulfur, and lead isotope studies

Jebel Mecella and Sidi Taya F–(BaPbZn) deposits are located within the Fluorite Zaghouan Province (NE Tunisia). The mineralization occurs along the unconformity surface between the Jurassic limestones and Upper Cretaceous rocks. The mineralization consists mainly of fluorite, barite, sphalerite, and galena. The δ34S values of barite at Jebel Mecella (14.8–15.4‰) and at Sidi Taya (21.6–22.2‰) closely match those of the Triassic evaporites and Messinian seawater, respectively. The range of δ34S values of galena and sphalerite in both deposits (−6.9 to +2.4‰) suggests the involvement of thermochemical sulfate reduction and possibly organically-bound sulfur in the generation of sulfur. Lead isotope data with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 18.893–18.903, 15.684–15.699, and 38.850–38.880, respectively suggests a single homogeneous source reservoir of Paleozoic age and/or the homogenization of the Paleozoic–Cretaceous multireservoir-derived fluids along their long migration paths to the loci of deposition during the Alpine orogeny.

An experimental study on metal precipitation driven by fluid mixing: implications for genesis of carbonate-hosted lead–zinc ore deposits

A type of carbonate-hosted lead–zinc (Pb–Zn) ore deposits, known as Mississippi Valley Type (MVT) deposits, constitutes an important category of lead–zinc ore deposits. Previous studies proposed a fluid-mixing model to account for metal precipitation mechanism of the MVT ore deposits, in which fluids with metal-chloride complexes happen to mix with fluids with reduced sulfur, producing metal sulfide deposition. In this hypothesis, however, the detailed chemical kinetic process of mixing reactions, and especially the controlling factors on the metal precipitation are not yet clearly stated. In this paper, a series of mixing experiments under ambient temperature and pressure conditions were conducted to simulate the fluid mixing process, by titrating the metal-chloride solutions, doping with or without dolomite, and using NaHS solution. Experimental results, combined with the thermodynamic calculations, suggest that H2S, rather than HS− or S2−, dominated the reactions of Pb and/or Zn precipitation during the fluid mixing process, in which metal precipitation was influenced by the stability of metal complexes and the pH. Given the constant concentrations of metal and total S in fluids, the pH was a primary factor controlling the Pb and/or Zn metal precipitation. This is because neutralizing or neutralized processes for the ore-forming fluids can cause instabilities of Pb and/or Zn chloride complexes and re-distribution of sulfur species, and thus can facilitate the hydrolysis of Pb and Zn ions and precipitation of sulfides. Therefore, a weakly acidic to neutral fluid environment is most favorable for the precipitation of Pb and Zn sulfides associated with the carbonate-hosted Pb–Zn deposits.

Giant Fluorite Mineralization in Central Mexico by Means of Exceptionally Low Salinity Fluids: An Unusual Style among MVT Deposits

The origin of the mineralization at the world-class Las Cuevas (the largest single fluorite deposit in the world) has been historically disputed, essentially between skarn-related and Mississippi Valley Type (MVT) models. A systematic study of fluid inclusions in these deposits revealed that they were formed by low temperature (49 to 177 °C) and low salinity (0 to 1.9 wt % NaCl equiv) fluids. The obtained δ13C (between −2.39 and 0.20‰ VPDB) and δ18O (between −14.03 and −7.37‰ VPDB) data from local host limestones agreed with regionally representative values in the literature. The obtained δ13C (between −15.60 and −12.99‰ VPDB) and δ18O (between −5.56 and −1.84‰ VPDB) data from hydrothermal calcite associated with fluorite mineralization indicated that the isotopic composition of hydrothermal fluids initially reflected buffering by the host rocks, and then recorded the interaction between meteoric water and basinal brines. It is likely that such processes occurred with concurrent maturation of organic matter, and that the obtained compositions may also have recorded a thermal effect on the local limestones. Halogen geochemical studies in inclusion fluids showed a distribution that suggests that solutes in mineralizing fluids were due to scavenging of Na+ and Cl− through water–rock interaction or halite dissolution, and that secondary sources would have been the evaporation or infiltration of seawater. The basinal brines with which the formation of these deposits was associated were massively diluted by deeply evolved meteoric water, thus making a significant fluorine input by basinal brines unlikely. Fluorine would have been provided by local groundwater through its interaction with Oligocene topaz rhyolites and other F-rich volcanic and hypabyssal rocks. Such a possibility is supported by present-day groundwater, which presents a regional endemic case of fluorosis. The precipitation of fluorite is possible at low temperatures (at which the solubility of this mineral is very low) by means of chemical reactions and physical interactions among very diluted F-poor basinal brines, F-rich groundwater, and host carbonate rocks. The latter systematically experienced hydrothermal karstification, which would have provided Ca2+ for reaction with F− and resulted in the precipitation of fluorite. This scenario stands for a depositional model that recalls those proposed for MVT and associated industrial mineral deposits, but is distinct from common models with regard to the primal source for fluorine and the extremely low salinities of inclusion fluids.

The Zn-Pb Mineralization of Florida Canyon, an Evaporite-Related Mississippi Valley-Type Deposit in the Bongará District, Northern Peru

AbstractThe Florida Canyon evaporite-related Zn-Pb sulfide deposit, in northern Peru, is one of the largest Mississippi Valley-type deposits in South America. Triassic carbonate and former evaporite-bearing rocks of the Pucará Group host the orebodies that constitute two different styles: (1) predominantly stratabound ore associated with hydrocarbon-rich porous dolostones and evaporite dissolution breccias and (2) high-grade ore associated with evaporite breccias representing diapiric injections along faults. A dome structure that controls the location of the ore deposit was defined by drill hole spatial data; the dome likely resulted from halokinetic processes during Andean deformation. NNE-trending, steeply dipping secondary faults linked to major northwest structures appear to control the distribution of ore grades in the deposit. Mineralization postdated hydrocarbon migration and accumulation. Strontium, carbon, and oxygen data isotope signatures allow distinction between pre- and synmineralization carbonate stages. The sulfur isotope composition of sulfides in the deposit suggests they precipitated as the result of mixing of a metal-rich fluid with resident hydrogen sulfide in the dome. Local thermochemical sulfate reduction may have contributed to the reduced sulfur budget during mineralization.

Trace Element Contents in Sphalerite from the Nayongzhi Zn-Pb Deposit, Northwestern Guizhou, China: Insights into Incorporation Mechanisms, Metallogenic Temperature and Ore Genesis

The Nayongzhi Zn-Pb deposit, located in the southeastern margin of the Sichuan-Yunnan-Guizhou (S-Y-G) Zn-Pb metallogenic province, China, has been recently discovered in this region and has an estimated resource of 1.52 Mt of metal at average grades of 4.82 wt % Zn and 0.57 wt % Pb. The ore bodies are hosted in the Lower Cambrian Qingxudong Formation dolostone and occur as stratiform, stratoid and steeply dipping veins. The predominant minerals are sphalerite, galena, dolomite, calcite with minor pyrite, and barite. In this paper, the inductively coupled plasma mass spectrometry (ICP-MS) technique has been used to investigate the concentrations of Fe, Cd, Ge, Ga, Cu, Pb, Ag, In, Sn, Sb, Co and Mn in bulk grain sphalerite from the Nayongzhi deposit, in an effort to provide significant insights into the element substitution mechanisms, ore-forming temperature and genesis of the deposit. This study shows that those trace elements (i.e., Cd, In, Sn, Sb, Fe, Mn, Cu, Ga, Ge, Ag, and Co) are present in the form of isomorphism in sphalerite, and strong binary correlation among some elements suggests direct substitution as Zn2+↔Fe2+ and coupled substitutions as Zn2+↔Ga3+ + (Cu, Ag)+ and Zn2+↔In3+ + Sn3+ + □ (vacancy), despite there being no clear evidence for the presence of Sn3+. Sphalerite from the Nayongzhi deposit is enriched in Cd, Ge and Ga and depleted in Fe, Mn, In and Co, which is similar to that of the Mississippi Valley-type (MVT) deposit and significantly different from that of the Volcanogenic Massive Sulfide (VMS) deposit, Sedimentary-exhalative (Sedex) deposit, skarn, and epithermal hydrothermal deposit. Moreover, the ore-forming temperature is relatively low, ranging from 100.5 to 164.4 °C, as calculated by the GGIMFis geothermometer. Geological characteristics, mineralogy and trace element contents of sphalerite suggest that the Nayongzhi deposit is a MVT deposit. In addition, according to the geological characteristics, Ag content in sphalerite, and Pb isotope evidence, the Nayongzhi deposit is distinct from the deposits associated with the Indosinian Orogeny in S-Y-G Zn-Pb metallogenic province (e.g., Huize, Daliangzi, Tianbaoshan and Tianqiao deposits), thus, suggesting that multi-stage Zn-Pb mineralization may have occurred in this region.

The role of hydrocarbons in ore formation at the Pillara Mississippi Valley-type Zn-Pb deposit, Canning Basin, Western Australia

Hydrocarbons have been suggested previously to play a role as reducing agents for in-situ sulfate reduction — one of several key components of the model proposed for ore formation in Mississippi-Valley-Type (MVT) deposits. Here, we provide direct evidence for hydrocarbon-brine interaction occurring synchronous to ore formation at the Pillara MVT deposit, through the analysis of brine and composite brine-hydrocarbon fluid inclusions by LA-ICP-MS combined with thermodynamic and reactive transport modeling. The occurrence of coeval primary hydrocarbon and brine inclusions in ore-stage calcite and sphalerite implicates the co-existence of hydrocarbons and brine at the time of ore formation. Elevated average concentrations (± 1σ) of 147 ± 141 ppm Zn, 53 ± 64 ppm Pb, 38 ± 36 ppm Cu and 11 ± 9 ppm Ag were measured in brine end member fluid inclusions. Hydrocarbon-bearing fluid inclusions are enriched several orders of magnitude in metal concentrations compared to the brine end member fluid inclusions. The analyzed fluid inclusion assemblages combined with numerical reactive transport simulations indicate that an oxidized acid-sulfate brine, which leached its metals from feldspathic sandstones in the deeper basin, represents a thermodynamically stable ore fluid. Interaction with feldspathic sandstones, granitic basement rocks and/or carbonates, and neutralization of pH, did not affect the Pb and Zn transport capabilities of the fluid. These findings indicate that Pb and Zn can be transported over long distances through carbonate-rich rocks, even though the original ore fluid may have been an acidic brine. The controlling factor for metal deposition at Pillara and similar MVT deposits can be related to the presence of hydrocarbons, permitting in-situ sulfate reduction and precipitation of sphalerite, galena, Ag and Cu sulfides.

Involvement of variably-sourced fluids during the formation and later overprinting of Paleoproterozoic Au-Cu mineralization: Insights gained from a fluid inclusion assemblage approach

Au-Cu mineralized quartz veins of the Reef Deposit, Wisconsin, USA, originally formed prior to or early in the Paleoproterozoic Penokean orogeny in central North America as either the root zone of a gold-rich VMS deposit, or in an orogenic gold setting. Nearly 400 m.y. later, magmatic hydrothermal fluids associated with a continental scale anorogenic magmatic event remobilized mineralization within the veins. And still later, during the Paleozoic, remobilization and perhaps upgrading of Au and other metals occurred in response to circulation of fluids associated with Mississippi Valley-type deposits found in overlying supracrustal rocks. Fluid constraints on the formation of the Reef Deposit and later overprinting over a 1.5 b.y. timeframe are examined using the fluid inclusion assemblage (FIA) approach. Distinctive assemblages are examined on individual merit, each offering individual stories to aid in our understanding of the protracted development of the Reef Deposit.Presumably primary fluid inclusions in Au- and Cu-bearing quartz-sulfide veins that formed during the Paleoproterozoic event show H2O-CO2-CH4 ± NaCl compositions based on microthermometry and laser Raman spectroscopy. Possibly primary H2O-NaCl and secondary H2O-CO2-CH4 -NaCl FIA formed prior to regional deformation and are recognized as discrete relict and neonate clusters. The intersection of isochores from the highest density neonate inclusions of either fluid composition indicates re-equilibration at lower amphibolite conditions during regional deformation. Quartz hosted secondary fluid inclusion assemblages characterized by H2O-CH4 and CO2-CH4 compositions formed at high temperatures and have not been re-equilibrated and are interpreted to post-date regional metamorphism. These FIA occur along healed fractures with chalcopyrite mineralization. These inclusions are likely associated with fluid circulation driven by emplacement of the adjacent Wolf River Batholith (ca. 1.45 Ga), that altered pyrite to pyrrhotite and remobilized or emplaced chalcopyrite at temperatures as high as 700 °C. This reduced fluid was in equilibrium with locally observed graphitic sediments. Secondary lower temperature (<50–210 °C) calcite and quartz hosted H2O-NaCl inclusions show variable homogenization temperatures and salinities. H2O-NaCl inclusions in quartz homogenize at 78–210 °C, with lower salinities of 3.0–13.9 wt% NaCl equivalent, and are observed to crosscut CH4 bearing FIA. H2O-NaCl inclusion assemblages in calcite have maximum homogenization temperatures of 103 °C and salinities of ~24 wt% NaCl equiv. Lower temperature H2O-NaCl inclusions are most likely related to the Paleozoic-aged MVT fluid overprint that remobilized and possibly emplaced gold mineralization.

Geochemical, isotopic, and fluid inclusion signatures of Zn-Pb mineralization in the Tiran mining district, Isfahan, Sanandaj-Sirjan zone (Iran)

In Tiran base-metal district, the post-Early Cretaceous epigenetic Zn-Pb deposits occur as fault-controlled pocket-like lenses. The main structural feature of mineralization is its association with a district-scale strike-slip fault, which cuts an en-echelon folded terrane. Mineralization occurs as sphalerite, galena, pyrite, and minor chalcopyrite found within massive ore, breccia textures, veins and veinlets, disseminated grains and carbonate replacements along tectonized limestone-shale contacts. The cumulative reserves of this district is 10 Mt grading at 6% Zn + Pb. Host rock silicification and calcitization formed during hydrothermal alteration. Fluid inclusion data revealed that ore minerals precipitated due to the mixing of two fluids, one determined from sphalerite-hosted inclusions (Homogenization temperature: 155 °C and salinity: 19 wt% NaClequiv.) and the other observed in quartz inclusions (Th: 184.5 °C and salinity: 12.5 wt% NaClequiv.). The sulfur isotope compositions of sulfide minerals vary between −8.92 and +4.15‰ and ranged from 22.61 to 23.88‰ for barite, thus suggesting an Early Tertiary marine sulfate influence. Sulfur isotopic data favor two sources of sulfur: bacteriogenic activity (δ34SCDT −9 to −6‰) and thermochemical sulfate reduction (δ34S: −1 to +4‰). The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios (18.1–18.4, 15.6–15.7, and 38.4–38.6, respectively) reflect upper crustal basement rocks as the source of metals. Fertile ore fluids mixed within fault zones, along the contacts of limestone and shale. Base metal deposition during fluid mixing could be a result of increasing reduced sulfur, cooling, and decreasing ligand activity after tectonic movements. The multiple lines of evidence presented here are consistent with the mineralization in the Tiran mining district being similar to Mississippi Valley-type deposits.

The carbonate-hosted MVT Morro Agudo Zn-Pb deposit, central Brazil

Morro Agudo is the largest known Mississippi-Valley Type deposit (MVT) in Brazil with original estimated reserves of 18.3 Mt @ 5.08% Zn and 1.75% Pb of which 3.92 Mt@ 4% Zn and 1.45% Pb remained in 2017. In spite of having been mined for more than 30 years, a comprehensive study of Morro Agudo metallogenic features was still lacking in the international literature. This deposit is hosted within the 250 km long Vazante Sequence, a N-S-trending Mesoproterozoic-Neoproterozoic carbonate-dominant sedimentary sequence thrusted over Neoproterozoic rocks during the Brasiliano Orogeny. Sulfide bodies in Morro Agudo are restricted to the Morro do Calcário Formation as a 1300 m long ore envelope averaging 9 m thick, comprising stacked up stratabound orebodies that thin out down dip and are limited to the NE by the Main Fault. Five orebodies are described: (a) Breccia-hosted orebody “GHI”, (b) Sphalerite-rich doloarenite orebody “JK”, (c) Galena-rich doloarenite orebody “L”; (d) Lower replaced stratiform orebody “M”; (e) Upper replaced stratiform orebody “N”. Comparison of these orebodies reveals mineral zonation patterns and variations in Zn-Pb grade consistent with sulfide textural relationships. These relationships indicate five mineralization styles that provide spatial and timing constraints for Morro Agudo; (a) Stratiform sulfides, (b) Massive Ore, (c) Laminated Ore, (d) Breccia-hosted Ore, (e) Late stage fracture-filling Ore. Carbon and oxygen stable isotope data for each mineralization style shows a pattern of mixing of signatures of mineralizing fluids and barren host rocks and supports our interpretation that these mineralization styles occurred in more than one stage of ore formation. The ore was later offset by a set of strike slip normal faults associated with compression related to the Brasiliano Orogeny, of which the Main Fault (Falha Principal) is the most important because it limits the deposit to the NE. Previous interpretation of upper orebodies as part of a SEDEX system is revisited in the present work. In our model, data used to support a syngenetic origin for Morro Agudo, such as synsedimentary structures, Pb isotopes in sulfides and fluid inclusion data indicate a younger, barren generation of sulfides deposited long before Zn-Pb mineralization, during sedimentation of the Morro do Calcário Formation in the Mesoproterozoic. These early sulfides were preserved in cherts and as massive pyrite beds that were later overprinted by sphalerite and galena. Overprinting thus mixed Meso and Neoproterozoic Pb isotopic sources and led to a long standing argument over whether the Morro Agudo ores were syngenetic or epigenetic. This interpretation is also in agreement with the current classification of the Vazante Sequence as containing imbricated Neoproterozoic and Mesoproterozoic sedimentary rocks. Based on our work of sulfide textural relationships, stable isotopes, whole-rock geochemistry and previously published data, we argue that Morro Agudo ores formed by at least two stages of percolation of mildly hot hydrothermal fluid in the Neoproterozoic. The primary reason for sulfide precipitation is interpreted to be mixing of mildly-hot, metal-bearing basinal brines and seawater/connate waters.